As a result of agricultural use of gray soils as arable land, instead fallow
horizon Ao and partly horizons A1 and A2 are formed arable Ap. Their
natural vegetation is disturbed soils, chemical composition in the upper
layers is changed, so soil is exposed to water erosion. Prolonged use gray
forest soils in agriculture led to their degradation, manifested by decreasing
organic matter mineralization due to its mechanical destruction of valuable
agronomic structure in the soil tillage process. Gray forest soils in Moldova
is characterized by a clear differentiation of the total chemical composition
of genetic horizons. In the composition of researched soils predominate
silicon compounds (SiO2), which make up 70-77%. In the arable gray soil
SiO2 content is higher by 3.56% in humus soil layer than in virgin soil of the
forest. Their vertical distribution in the soil profile have an accumulative
characteristic in humus horizon of soil and partial in the parental rock.
Global chemical composition of typical gray soils as hereditary property of
native rock is altered by the action of elementary processes and their use in
arable soil. Changing the chemical composition of the soil horizons can be
identified by comparing the total chemical composition of the rocks that
have been formed. The mineral part of typical gray soil is composed of
silicates and sesquioxides. Share of oxides of manganese, titanium, sulfur,
phosphorus, potassium and sodium constitute an insignificant part.
According relatively content in the typical gray soils oxides are located in
the following series: SiO2→ Al2O3→ Fe2O3→ K2O→ Na2O→ CaO→
MgO→ TiO2→ SO3→ MnO→ P2O5. Utilization of forest gray soil in
agriculture led to changes in their chemical composition in the upper
humiferous horizon. To improve fertility of arable gray soils in is necessary
measures to increase organic matter in arable layer, remediation of
structure formation, erosion protection and other anthropogenic factors.